Borrowings Borrowings - (Narrative) (Details) - USD ($) $ in Billions	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Total borrowings	$ 2.5	$ 4.0

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

No definition available.

Name:	us-gaap_DebtLongtermAndShorttermCombinedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant